Local interconnect structures have been proposed by many technologists as a low resistance "short" interconnect for signals. The resistance is typically about 1 to 10 ohms/sq. The most common proposed structures have been Ti/TiN and Ti/Si structures. The Ti/TiN suffers in performance because it is at the high end of the resistance specification. The Ti/Si structure has the right resistance of &lt;3 ohms/sq, but the problem is that the stoichiometry is very critical. It appears a ratio of between 0.1 to 0.4 for Ti to Si is desirable. Any ratio outside of the range will cause peeling.
An added problem for the Ti/Si structure is that in most applications, it is required that three different types of silicide be formed at the same time; namely, silicide on polycrystalline films, silicide on single crystalline, and silicide on amorphous films. The simultaneous optimization of (a) deposition of Ti:Si and (b) formation of these three levels of silicide is close to impossible for all practical purposes. A side effect of the inability for the simultaneous optimization is that the silicide film(s) will delaminate from the underlying layer due to intrinsic stress problems of the silicide. The incorporation of other foreign elements such as oxygen exacerbates the problem by impeding the silicidation reaction and increasing the intrinsic stress.
Therefore, a new interconnect structure is required to provide applicable solutions. The invention disclosed herein provides that solution.